Pages

Thursday, 4 November 2010

Hologram Messages? Closer?

Star Wars-style holograms: a new hope?

Novel plastic could enable real-time 3D holographic projections.

Zeeya Merali

Princess Leia could soon be beamed into a room near you.LUCASFILM/20TH CENTURY FOX/THE KOBAL COLLECTION

The fuzzy three-dimensional (3D) image of Princess Leia calling for help in the 1977 film Star Wars demonstrates an effect that researchers have long been trying to achieve: holograms that move in real time. Now, a material that can store shifting holographic data moves the fantasy into the realms of reality. The substance could have future applications in medicine and manufacturing, as well as in the entertainment industry.

"From day one, I thought about the hologram of Princess Leia and whether it can be brought out of science fiction," says Nasser Peyghambarian, an optical scientist at the University of Arizona in Tucson, who has been trying for several years to develop holographic projections that move in real time.

The challenge was to find a rewritable material that could store data encoding successive holographic images. Now Peyghambarian and his colleagues have developed a material that can record and display 3D images that refresh every two seconds. The research is published inNature this week 1.

The team's system captures 3D information by filming an object from multiple angles, using 16 cameras that each take an image of the object every second. The 16 views are processed into holographic pixel data by a computer, which sends a signal to two pulsed laser beams that then write the data into the recording material.

During the writing process, the two beams combine to create an interference pattern of light and dark patches in the recording material. Firing another light at the pattern reconstructs the 3D image.

Electron drift

In a static hologram, the physical properties of the recording material are permanently changed by this interference pattern, so the image can never be refreshed. In contrast, Peyghambarian's team has developed a rewritable recording material from a combination of plastic polymers, dubbed PATPD/CAAN. When the laser beams hit the copolymer, they cause electrons and other charge carriers within it to drift and gather in areas corresponding to dark and light regions of the interference pattern, creating a temporary recording. The stored image can then be overwritten by the next round of image data to be displayed.

“Creating a dynamic hologram of the size and resolution of Princess Leia is a reality.”

In 2008, the team used a similar material to build a 4-inch display that took about 4 minutes to overwrite 2. Now, they have modified the mix of polymers to develop a 17-inch display that refreshes more than a hundred times faster, generating an image that changes in almost "real time", says Peyghambarian.

Although 3D televisions are already on the market, these are filmed from just two perspectives. So they give a sense of depth, but "you cannot walk around an image of a person and see the back of his head", says Peyghambarian.

He hopes that, along with revolutionizing entertainment, the hologram technique will one day enable surgeons to remotely view live 3D images of operations and give advice. It might also find uses in manufacturing, allowing engineers to visualize and modify 3D models in real time.

360 degrees

However, Rob Eason, an optical physicist at the University of Southampton, UK, points out that the holographic images are still relatively slow and small, and questions whether the technique significantly improves on other recent advances in 3D displays. In 2009, for example, Sony unveiled a prototype called RayModeller. It projects a moving 3D image within a cylindrical tube, allowing the viewer to walk all the way around it and see different perspectives.

ADVERTISEMENT

Peyghambarian counters that a scaled-up holographic system would provide "superb resolution. We can already make a holographic pixel of 400 micrometres — better than a high-definition television."

He adds that it should be easy in principle to record holographic movies, so they can be played back later. The team is now working to speed up the refresh rate to match the 30 frames per second needed for movies, and to reduce the amount of power needed to read and write images.

Peyghambarian believes that some version of the system could be in homes within seven to ten years: "We have shown that creating a dynamic hologram of the size and resolution of Princess Leia is a reality." Now he just needs to build an R2-D2 to play it on.